A typical oil and gas well includes a casing string cemented in place between inside a hole bored through a hydrocarbon bearing formation. As used hereinafter, hydrocarbon is used to denote oil, gas, and any mixture thereof. In order for hydrocarbons to flow into the well bore, the casing is perforated in the interval containing the hydrocarbons. The high pressure jet from modern perforating guns pierces the casing and forms a hole by pulverizing cement and formation into compacted particles. Cement and material from the jet charge may fill the perforation tunnel. It is necessary to remove this debris from the perforation tunnel to increase the flow of hydrocarbons into the well bore.
In the usual course of producing hydrocarbons from an oil or gas well (hereinafter collectively referred to as "oil well"), paraffin contained in the oil may clog the perforations and casing. Scale comprised of various carbonates may precipitate out of solution from brine produced with the hydrocarbons and clog the perforations and well bore.
Prior art methods for cleaning and stimulating wells have included acidizing, re-perforating, fracturing with explosives and fracturing with hydraulic pressure. Such techniques have been used advantageously but have a number of significant disadvantages, not the least of which have resulted in introduction of foreign material such as acid and sand particles into the well. Prior art methods of cleaning have also included mechanical scrapers and hydraulic activated knives as taught in U.S. Pat. No. 2,574,141.
It has been suggested in the prior art to use acoustic energy for stimulating producing wells. A fluidic oscillator may be used to create pressure fluctuations to induce stress in the walls of the perforation tunnel, thereby increasing production and cleaning perforations as disclosed in U.S. Pat. Nos. 5,135,0531 and 5,228,508 issued to Facteau. The pressure fluctuations of the Facteau tool are generated from an oscillation chamber with two outlet ports. A similar fluidic oscillation chamber with dual outlet ports is disclosed in U.S. Pat. No. 5,165,438 also issued to Facteau.
Another stimulation tool using acoustic energy is disclosed in U.S. Pat. No. 3,520,362 issued to Galle.
Although the above recited tools seemed feasible, there exists a practical difficulty of delivering sufficient acoustic power to the producing formation for the desired stimulation and/or to the area desired to be cleaned.
As disclosed in IADC SPE paper 27468, and in Republic of China Patent No. 89201391, Helmholtz oscillator theory has been suggested for generating a pulsating jet flow in the jet nozzles in bits used in drilling oil wells as a means for improved hole cleaning and faster drilling rates. Pulsed high pressure water jets are known to have advantages over continuous jet streams for use in cutting materials, especially brittle materials. By exerting an alternating load on materials, pulsed jets can produce not only extremely high momentary pressures (i.e. water hammer effect) in the materials, but also absolute tensile stress, which gives rise to unloading destruction of brittle materials, through reflection of the stress waves.
The present invention applies Helmholtz jet technology in wells after the drilling phase (i.e. during initial cleaning and stimulation of new well and during remedial cleaning and stimulation of existing wells).